People pay more attention on housing security with the social progress and technical development. A door closer is a mechanism which allows a door to close automatically. The closer usually extends between the door and door frame, and will close the door automatically under the resilient restoring force of the door closer, thereby ensuring that the door is returned to the original position accurately and timely after the door is open. The door closer provides convenience in daily life.
However, prior art door closers, such as mechanical spring door closer, usually generate a large impact force when closing the door, whereby people are easily bumped by the door because they cannot dodge or escape the closing door in a timely manner. Sometimes a big impact noise will occur when the door is closed. In addition, failure of the door closer may occur due to the instability of the spring.
In order to solve these problems, a full hydraulic door closer and an oil-air hybrid driven door closer have been developed to adjust the process of opening/closing the door according to requirements of users, while the door body and the door frame are protected effectively.
But the full hydraulic door closer and the oil-air hybrid driven door closer in the prior art have drawbacks as follows:
1. Oil leakage occurs frequently during the use, causing problems, for example, the door cannot be closed fully;
2. The speed of closing the door is controlled by oil or fluid. The biggest problem of such technology is that viscosity of the oil varies with the changes of air temperature, which will influence the flowing rate of oil, and thus the speed of closing the door. In other words, provided in the same adjustable position, the speeds of closing the door are different in winter and summer, especially for the exterior door. Accordingly, it is usually required to adjust the control apparatus of door closer, which may bother users;
3. The oil-air hybrid driven door closer is provided with a control valve in air communication with the atmosphere. The dusts mixed in the air will easily enter the oil cavity of the cylinder, causing a larger oil viscosity of hydraulic oil in the oil cavity. Thus, the speed of closing the door will be affected. Also, the service life of the oil cavity of the door closer will be shorter due to dust contamination and friction.
Therefore, a primary objective of the present invention is the provision of an improved pneumatic door closer which overcomes the problems of the prior art.
Another objective of the present invention is the provision of a pneumatic door closer having a gas chamber with a sliding piston therein, wherein gas flows within the chamber to opposite sides of the piston as the door opens and closes.